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December 03, 2010

Some Grains of Salt For a Halophile

The geekosphere has been buzzing over yesterday's announcement from NASA about the discovery of arsenic-based life. Specifically, a species of single-celled archaean living in hyper-salty, hyper-alkaline, arsenic-laced Mono Lake in California can actually use arsenic instead of phosphorus in its biological processes. If you Google it, there are already thousands of articles talking about how this dramatically expands the possibilities for life beyond Earth. In other words, we have an example of Life Not As We Know It.

Right?

Well . . . no.

The newly-discovered archaean (strain GFAJ-1 of the newly-discovered Halomonadaceae family) isn't alien life at all. It's 100% true-blue native-born Earth life, a very very very distant cousin of most of the people reading this 'blog post. And that's a very important thing to keep in mind.

Here's why: the Halomonadaceae didn't evolve out of prebiotic molecules in the hostile environment of Mono Lake. They're descended from much more ordinary archaeans, which presumanbly had normal arsenic-free DNA and other chemical machinery. The Halomonadaceae evolved the ability to live and thrive in the horrible water of Mono Lake, but they are descended from life forms which started out in a much more benign environment.

This is important because it means life may be able to survive in all kinds of strange and extreme environments, but it says almost nothing about what kind of conditions you need to start life in the first place. By analogy: one could find humans on the Moon in 1969. That doesn't mean humans evolved there. So if at some point we find a planet covered with Mono Lake water, I wouldn't expect to find alien organisms resembling GFAJ-1 there -- unless somewhere, at some point in the planet's history there were lakes or seas without so much poison. Life is tenacious and adaptable, but it's hard to create.

On the other hand, the fact that GFAJ-1 can apparently build DNA using arsenic rather than phosphorus means there is likely a wider range of possible genetic molecules than biologists had expected. There may well be organisms elsewhere in the Galaxy which use very different molecules as the "information storage medium" for their genes.

Comments

"On the other hand, the fact that GFAJ-1 can apparently build DNA using arsenic rather than phosphorus means there is likely a wider range of possible genetic molecules than biologists had expected. There may well be organisms elsewhere in the Galaxy which use very different molecules as the "information storage medium" for their genes."

Which, at least to me, is a huge deal. I get pissy with the media trying to make this something that it's not to make it feel bidder than it is when what it is is pretty damn big. But I still want people to acknowledge that it is pretty damn big.

Then again, anything that looks like it's shifting the Drake Equation in favor of contacting extraterrestrial life is OK by me.